The present invention relates to an apparatus and system for transmitting and/or receiving steadily generated data such as video data, audio data, and the like via a network.
Upon transmitting/receiving data via a network, the output rate of data onto the network is important. That is, if data is output beyond the transmission capacity that can be used in the network, data losses occur; if the output rate is too low, the usable band of the network cannot be sufficiently used, and required quality cannot be obtained. In such case, data losses on the network are monitored to adjust the output rate, and if losses occur, the output rate is lowered.
A large number of notes are distributed between the transmitting and receiving sides on the network, and respectively have buffers that can save data. Hence, when data has been excessively output and losses have taken place, some of buffers on the network are likely to have overflown. Even when the output rate is lowered after the losses have actually occurred, since buffers somewhere on the network are already full of data, data output from the transmitting side reaches the receiving side with a transmission delay corresponding to the time required for processing the data saved in such buffers by the network, thus posing a serious problem in data communications that requires real-time processing.
That is, data is required to be output at an output rate that satisfactorily use the available network band while suppressing a transmission delay below a given value.
As described above, when two end terminals exchange data via the network, some data which were output onto the network have not arrived the receiving side since they are still present on the buffers in intermediate nodes on the network or the transmission lines. Since data which stay in the buffers in the intermediate nodes may also cause a transmission delay, the output rate must be controlled to prevent such data volume from becoming too large, so as to suppress any transmission delay below the given value. However, the transmitting and receiving terminals cannot detect the volume of data that stay in the buffers in the intermediate nodes on the network, especially, on the internet.
It is an object of the present invention to provide a data communication apparatus, method, system, and storage medium, which can reduce deterioration in the real time communication caused by the volume of unarrived data on the network.
It is another object of the present invention to provide a data communication apparatus, method, system, and storage medium, which perform data communications at an optimal transfer rate on the basis of the volume of unarrived data on the network present between two end terminals.
It is another object of the present invention to provide a data communication apparatus, receiving apparatus, control method, storage medium, and data communication system, which can realize optimal data transfer by dynamically controlling to change the transfer rate in correspondence with the conditions on the network in data communications via the network.
The present invention has been made in consideration of the above situation, and has as its still another object to provide a video communication system, video transmitting apparatus, video receiving apparatus, their control method, and storage medium, which can efficiently transfer video data by appropriately adjusting the transfer rate of video data by fully utilizing the transmission band of the network.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.